The demand for increased oil production has brought about a need for a longer stroking pumping unit. Where this need is accomplished by a pumpjack unit, the cost of such longer stroking pumping units is exhorbitant because the pumpjack unit must necessarily be of gigantic proportions in order that a long rocking beam be sufficiently elevated into the air by the Sampson post such that the polish rod reciprocates a considerable distance to thereby impart a long stroke into a subsurface pump.
In my previously issued U.S. Pat No. 3,096,717, issued July 9, 1963, there is taught improvements in a well pump of which a sucker rod stroke of a given length is caused to move a pumping piston through a much longer stroke to thereby achieve the benefits of long stroke pump operation, while utilizing a relatively short sucker rod stroke. In this particular hydraulically operated pump apparatus, the arrangement of the engine respective to the subsurface pump results in insufficient tension being effected within the sucker rod string during the downstroke cycle. This type of system induces rod breakage because of accumulation of gaseous fluid under the lift piston of the engine. The gaseous hydrocarbons separate from the production fluid and enter under the lift piston or the power piston, thereby preventing an optimum stroke to be imparted into the subsurface pump. This condition promotes rod breaks, as well as accelerated wear of the various other moving parts. It also greatly reduces pumping efficiency, and in its most aggravated form, harmonic motion may be induced within the rod string which causes various components of the system to get out of phase with one another, ultimately causing failure of the components thereof.
Accordingly, it is desirable to provide a downhole hydraulically actuated pump assembly, which is operated in conjunction with a pumpjack unit, and wherein the entire pumping unit, except for the pumpjack, is located within the borehole. This desirable expedient prevents contamination of the surrounding geographical location with crude oil, should any leaks develop therein. It is also desirable to provide a low cost, longer stroking pump unit which provides a greater subsurface pump stroke with respect to the stroke of the polish rod. It is further desirable that such a pump maintain the entire sucker rod string in tension during both the upstroke and the downstroke.